Prior art includes the Conical Beam Concentrator RT:C, U.S. Pat. No. 4,575,196, by this inventor. This concentrator consists of six annular sectional lenses which are integrally adjoined to form one lens. Metal louvers mounted outside the concentrator must be used to intercept radiation which is extraneous to the perpendicular incipient beam.
The code designation of the louvered conical beam concentrator is RT:C (R--refracting section of a component lens, T--transmitting section of a component lens, and C--concentrating lens).